1. Technical Field
This invention relates generally to maximizing the efficiency of radio frequency power amplification in a wireless communication device transmitter, and, more particularly, to a high efficiency multiple power level amplifier.
2. Related Art
With the increasing availability of efficient, low cost electronic modules, mobile communication systems are becoming more and more widespread. For example, there are many variations of communication schemes in which various frequencies, transmission schemes, modulation techniques and communication protocols are used to provide two-way voice and data communications in a handheld telephone-like communication handset. While the different modulation and transmission schemes each have advantages and disadvantages, one common factor is the need for highly efficient power amplification. As these communication devices become smaller and smaller, the functionality provided by these devices continues to increase. One major concern when developing these handheld communication devices is power consumption. As the devices become smaller and smaller, the amount of power consumed and dissipated becomes more and more critical. High efficiency power amplification decreases the amount of power consumed, thereby maximizing battery life of the device.
Another major concern in these wireless devices is the size of the circuitry. In order to minimize the hardware required it is desirable to integrate as much functionality as possible into fewer and fewer circuit modules. This enables the hand held device to be smaller and consume less power.
Most wireless power amplifier applications require high efficiency over a broad range of operating power levels. This is inherently difficult to achieve without circuitry and logic in addition to the power amplifier. Typically, additional circuitry residing on a control die must be used in addition to the power amplifier circuit.
One conventional manner in which to achieve high efficiency power amplification over a broad range of power output levels uses radio frequency (RF) switches to select different power amplifiers based upon the required power output demand. Each of the power amplifiers can be optimized for high efficiency at different power levels. Unfortunately, this solution requires the use of an additional control die in which to house the RF switches.
Another conventional manner in which to achieve high efficiency power amplification over a broad range of power output levels involves two separate amplifiers having different characteristics, each optimized for high efficiency at different power levels. In such an arrangement, the amplifiers are activated individually to satisfy the required power levels. Microwave couplers are used to ensure the correct phase match between the two amplifiers. Unfortunately, this approach still requires a separate control die and is difficult to achieve in commercial high-volume applications. Furthermore, the two different amplifiers must have a matched phase supplied at their input, thereby requiring that the microwave couplers be extremely stable.
Therefore, there is a need in the industry for a wireless power amplification circuit that achieves highly efficient power amplification over a broad range of output power levels and that is economical to produce in high volume.
The invention provides a high efficiency multiple power level amplifier that maximizes power amplifier efficiency and minimizes the required control circuitry. The invention maximizes the efficiency of a power amplifier circuit and simultaneously minimizes the amount of control circuitry required to control the amplifier. Two amplifiers having similar amplification characteristics are connected to two RF couplers. The isolated port of each RF coupler is connected to an impedance modification circuit. The power amplifier circuit can use both amplifiers when power demand is high and use the output of a single power amplifier when power demand is lower. When using only one power amplifier, the impedance modification circuit eliminates the impedance mismatch caused by the single power amplifier operation by using an externally biased semiconductor to present the proper impedance to the coupler connected to the inactive power amplifier. In this manner, any impedance mismatch between the operative and inoperative power amplifiers is compensated, thus allowing the single operating power amplifier to achieve optimal performance.
Related methods of operation and computer readable media are also provided. Other systems, methods, features, and advantages of the invention will be or become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.